There are many different types of sprinkler constructions used for irrigation purposes, including impact or impulse drive sprinklers, motor driven sprinklers, and rotating reaction drive sprinklers. Included in the category of rotating reaction drive sprinklers are a species of sprinklers known as spinner or a rotary sprinklers which are often used in the irrigation of agricultural crops and orchards. Typically, such spinner type sprinklers comprise a stationary support structure or frame which is adapted to be coupled with a supply of pressurized water, and a rotatable deflector supported by the frame for rotation about a generally vertical axis. Most rotary type sprinklers employ either a rotating reaction drive nozzle or a fixed nozzle which ejects a stream of water vertically onto a rotating deflector. The deflector redirects the stream into a generally horizontal spray and the deflector is rotated by a reaction force created by the impinging stream from the fixed nozzle.
One shortcoming that has been encountered with rotary-type sprinklers is that due to a very high rate of rotation of the rotary devices, the distance the water is thrown from the sprinkler may be substantially reduced. This has created a need to control or regulate the rotational speed of the deflector and thereby also regulate the speed at which the water streams are swept over the surrounding terrain area. A relatively slow deflector rotational speed is desired to maximize throw-distance, and therefore a variety of brake devices have been developed to accomplish this end.
In one approach, a viscous brake device is used to control rotation of the deflector. The viscous brake device utilizes drag produced by rotation of a brake rotor within a viscous fluid. While suitable for some sprinklers, the viscous brake device may not provide constant rotation speed when the ambient temperature or supply pressure changes.
Another shortcoming encountered with rotary-type sprinklers is that the sprinklers have frame supports that interfere with the water stream after it has been redirected by the deflector. There have been a number of attempts to minimize this interference including utilizing supports with different cross-sectional shapes. However, even with these approaches, the water stream still impacts the supports every time the deflector completes a rotation. This produces a reduced, but still present, shadow in the spray pattern of the sprinkler.
Yet another shortcoming of some prior rotary-type sprinklers is the serviceability of the sprinkler. Rotary-type sprinklers often have two typical types of failures that require the sprinkler to be removed from the water supply in order to be fixed. The first type of failure occurs when the nozzle becomes plugged with debris from the water supply. For some sprinklers, the nozzle is installed from the underside of the sprinkler such that the sprinkler needs to be removed from the water supply in order to remove and clean the nozzle. The second type of failure occurs when the deflector of the sprinkler stops rotating or spins out of control. In this case, the braking system has failed and the entire sprinkler will be replaced.
Some prior sprinklers utilize viscous braking to control the rotational speed of the deflectors of the sprinklers. One problem with this approach is that the viscosity of the working fluid changes inversely with temperature. As a result, the deflector rotates faster as temperature increases, and slower as the temperature decreases. This change in rotational speed may negatively affect the area that is covered by the sprinkler, or it may cause the deflector to stall during low temperature conditions when coupled with low pressure operation.